Thanks to you all, great in-put.
I was going to make one from a set screw, but a set screw does not have that small shoulder that would stop the screw from going completley thru the barrel.
I know I could make it work, but the gun is for a friend and I have no idea who may someday try removing and re-installing the liner, and maybe go in to far.
My first mistake was in taping it whole way thru.
In the past I have stopped the threads a little short of entirely thru, then the screw / liner could only go so far.
But I see that TOW has basically the same thing as the LIGHTNING but in 1/4 X 28 threads which will work perfectly I think.
Thanks again to all